Paving machines are generally used for laying heated paving material, such as, bituminous aggregate mixtures or asphalt, onto a roadbed or a paving surface. After heated asphalt is laid, it is typically spread, leveled, compacted and cooled to achieve a road with a uniform and smooth surface passable by vehicles. To compact and spread the heated asphalt, the paving machine typically employs a screed assembly. The screed assembly can be self-propelled or be pulled by tractors, trucks or other similar equipment. The screed assembly may include one or more screed sections that may receive a supply of asphalt from the truck or tractor and may heat, vibrate and/or manipulate the asphalt into a smooth uniform surface.
Often, the screed assembly includes two main screed sections in the center of the screed assembly, and hydraulically extendable screed extenders connected to the sides of the main screed sections for greater paving widths. In addition to the main screed sections and the screed extenders, bolt-on extensions may be connected to the screed extenders for paving even larger areas. For example, for paving an area greater than five meters, six or more screed sections including, two main screed sections, two screed extenders and two or more bolt-on extensions may be employed.
To improve the asphalt compacting and spreading capability of the various screed sections, screed assemblies often utilize a tamping mechanism. The tamping mechanism may pre-compact the asphalt before delivering the asphalt to a screed plate. The tamping mechanism may include a tamper bar and a wear bar on each screed section. The tamper bar may pre-compact and feed the asphalt under the screed plate for effective spreading and further compacting on the paving surface. The wear bar, on the other hand, may be found behind the tamper bar and may be mounted to a screed frame such that a bottom surface of the wear bar is substantially aligned with a bottom surface of the screed plate. The wear bar minimizes wear and tear to the screed plate and the screed frame to which the wear bar is mounted to.
The wear bar, which is a replaceable component, is generally mounted to the screed frame such that a bottom edge of the wear bar is above the bottom edge of the screed plate. In other words, the wear bar maintains a height tolerance relative to the bottom (asphalt finishing surface) plane of the screed plate. Such a height tolerance is often desired to prevent the wear bar from protruding or otherwise extending beyond the bottom edge of the screed plate (and therefore the screed section) and, thus, leaving a pattern or deft mark on the paving surface as the associated screed section compacts and spreads the asphalt.
Specifically, if the wear bar protrudes below the screed plate, asphalt may potentially stick to the wear bar causing an irregularity (i.e. drag marks, gouges, and segregation of material) in the finished asphalt surface. Such irregularity may also be present in the final asphalt surface if the wear bar is above the screed plate by more than one millimeter. For example, a rock may get stuck or catch the edge of the screed plate leading to variations in the surface texture of the road. Thus, the height tolerance of the wear bar relative to the screed plate is maintained anywhere from a zero millimeters (0 mm) or flush to a one millimeter (1 mm) above the bottom edge of the screed plate.
Since the wear bar is a replaceable component, the height tolerance is required to be maintained every time the old wear bar or old screed plate is replaced and a new wear bar or new screed plate is mounted to the screed frame. Maintaining this height tolerance is challenging, particularly because of the tolerance stack-up between the screed plate and the screed frame or due to assembling a worn wear bar with a new screed plate (or a new wear bar with a worn screed plate). One prior art solution to maintain the height tolerance involves mounting the wear bar to the frame and then grinding any part of the wear bar that protrudes below the screed plate. For a standard sized wear bar being mounted to a thicker screed plate, lesser grinding may be needed (because a smaller portion of the wear bar may extend beyond the screed plate), while additional grinding may be needed for thinner screed plate. Such grinding not only takes time, it increases labor costs and at least somewhat compromises the structural integrity of the wear bar.
Another prior art solution involves lining up the wear bar in the correct location against the screed frame and drilling holes through both the wear bar and the screed frame and connecting with fasteners. This technique is typically not employed because of the time and costs involved in drilling holes on the assembly line. Furthermore, drilling is not a favorable process to perform on the assembly line.
Yet another prior art solution for varying heights is discussed in U.S. Pat. No. 3,262,378 issued to Schrimper et al. for adjusting the height of a strike-off plate extending downwardly from a mold board of a screed. The patent employs an adjusting means having at least two adjusting members fixed to the strike-off plate at spaced locations thereof. The adjusting means varies the height of the strike-off plate by one half an inch from a central position by way of a shoulder bolt threaded into a front wall of a screed section. The shoulder portion of the bolt passes through a vertical slot such that by varying the position of the shoulder bolt within the vertical slot, the height of the strike-off plate may be varied. Such a height varying mechanism may not work effectively for a wear plate, especially since the height of the wear bar is not constantly changed unlike a strike-off plate. Furthermore, a shoulder bolt varying in position within a vertical slot may not be sufficient to maintain the desired height tolerance for an extended period of time.
It would accordingly be beneficial if an improved mechanism for effectively mounting the wear bar to the screed frame while maintaining the desired height tolerance with the screed plate can be achieved. It will additionally be beneficial if the mechanism maintained the height tolerance irrespective of the varying thicknesses of the screed plate.